package task01;
import java.lang.*;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int n,sum=0;
		while(sc.hasNext()) {
			n = sc.nextInt();
			System.out.println(SUM(n));
			System.out.println();
		}
		
	}
	
	public static int SUM(int n) {
		int sum=0;
		for(int i=0;i<=n;++i) {
			sum+=i;
		}
		return sum;
	}

}
